1. Field of the Invention
The invention relates to an operating microscope for observing an operating field, which includes an image display device for displaying an image derived from registered image data, and an optical system for combining the derived image with the observation of the operating field.
2. Description of the Related Art
An operating microscope of this kind is known from the article "A frameless stereotaxic integration of computerized tomographic imaging and the operating microscope" in Journal of Neurosurgery 65 (1986), pp. 545-549.
The known operating microscope comprises an imaging device which includes a miniature black and white display screen on which a contour of a relevant part of the operating field is displayed. The imaging device also comprises a beam splitter whereby the contour displayed on the miniature display screen and the actual operating field are simultaneously visualized for the user of the operating microscope. Using an arithmetic device, the contour of the relevant part, for example a tumor to be removed, in the operating field is derived from image data (CT data) previously registered by means of an X-ray computerized tomography device. A drawback of the known operating microscope consists in that during observation of the actual operating field only a limited image data visualization, containing two-dimensional information, is available to the user.
For projection of the contour derived from the CT data it is necessary to register the CT data and the optical axis of the microscope in a common coordinate system. From the cited article it is known to provide fiducial markers on the patient to be examined for this purpose. The markers are non-transparent to X-rays and are taken up in the CT data. The position of the operating microscope is determined by means of a three-dimensional acoustic referencing system which utilizes an acoustic localizer which generates ultrasonic pulses in a spark gap of a spark plug attached to the operating microscope. The ultrasonic pulses are picked up by three microphones which are mounted on a stand and which determine the coordinate system in the operating room. At the beginning of an operation the operating microscope is successively directed to the markers and the successive positions of the operating microscope are registered in the coordinate system by the acoustic localizer. For a new setting of the operating microscope, involving selection of a new focal plane, the position of the operating microscope should again be determined by means of the acoustic referencing system. From the CT data there are subsequently derived image data which correspond to a slice of the patient in the focal plane whereto the operating microscope is adjusted, and from these image data a contour of relevant structures, for example a tumor, is derived.